The goal of this study is to further the understanding of the fundamental biology of adult angioblasts and to use this knowledge to test therapeutic strategies in the treatment of peripheral vascular disease. Peripheral vascular disease, stroke, diabetes, burns, and severe trauma are all characterized by impaired circulation. Conventional drug therapies to restore circulation have been only modestly successful, and it is to too soon to determine the extent of clinical gene therapy trials. Interestingly, the use of exogenous endothelial cells to augment new blood vessel growth is relatively untested. Recently it was found that peripheral blood contains cells that can differentiate into endothelial cells in vitro, incorporate into new blood vessels in vivo, and persist in the mouse for at least 6wk. This work is a first step in determining if these putative circulating endothelial cell precursors, called angioblasts, can be used to augment new blood vessel growth clinically. The long-term goal is to develop a procedure in which cells with embryonic-like differentiation capabilities can be retrieved from a patient, proliferated ex vivo, and returned to the patient, such that each patient becomes their own endothelial cell donor. In this study, angioblasts will be isolated in large numbers and factors that control their growth and differentiation will be investigated. Means to facilitate their use to enhance blood vessel growth in an ischemic limb model in both non-diabetic and diabetic mice will be developed. Because diabetes profoundly exacerbates macro- and microvascular disease, use of diabetic mice will provide a more stringent test of angioblast potential than would normal mice. We will also investigate the involvement of angioblasts in retinal vascularization to assess the possibility that anti-angioblast therapy may be an effective means of inhibiting proliferative retinopathy.